This invention relates generally to fiber reinforced thermoplastic polymer sheets, and more particularly to decorative multi-layer structures containing porous fiber reinforced thermoplastic polymer sheets.
Porous fiber reinforced thermoplastic sheets have been described in U.S. Pat. Nos. 4,978,489 and 4,670,331 and are used in numerous and varied applications in the product manufacturing industry because of the ease molding the fiber reinforced thermoplastic sheets into articles. Known techniques, for example, thermo-stamping, compression molding, and thermoforming have been used to successfully form articles from fiber reinforced thermoplastic sheets.
Porous fiber reinforced thermoplastic sheets are sometimes formed into decorative interior sound absorbing panels for use in the interior of automobiles, mass transit vehicles, and buildings including commercial buildings and private buildings. These interior sound absorbing panels typically include a decorative layer on one side for aesthetics. To achieve the greatest percentage of sound absorption at frequencies less than 10,000 hertz, air is permitted to flow into the porous fiber reinforced sheet. In certain automotive market segments, sound absorbing panels, for example, headliners, are made air impermeable to preclude the preferential deposition of cigarette smoke and ash in the panel where the opposite side of the panel is open for air circulation.
Noise problems can occur when design clearances between the airflow terminating layer and the sound absorbing panel's supporting structure are small. Vibrations occurring to the sound absorbing panel can create undesirable noise caused by the panel contacting the support structure. One way that has been used to reduce undesirable noise is to increase the design clearance between the air terminating layer and the panel support structure. However, this approach can require additional design costs and tooling modifications. It also reduces the size of the interior compartment of an automobile.
Also, adhesive bonding of additional components to the airflow terminating layer can present adhesion problems. The shear strength at the adhesive bond line during and after exposure to heat aging can become insufficient to maintain a desirable bond strength. Scoring the airflow terminating layer has been used to increase bond strength but the scoring can lesson the effectiveness of the airflow terminating layer and causes increased production costs. Also, a two step adhesive process is sometimes used where the airflow terminating layer is primed or chemically treated before the adhesive application.